Physician Focus: The power of vitamin D

Dr. David C. Dodson

Tuesday

Dec 29, 2009 at 12:01 AMDec 29, 2009 at 5:31 PM

Vitamin D has come a long way in a short time. When I was a medical student in the 1970s, all that was known about this nutrient was that it helped to absorb dietary calcium. We now know that every cell in our bodies contains receptors for vitamin D and that vitamin D modifies the activity of about 10,000 genes, or about one third of the human genome. Vitamin D, it seems, does an enormous amount of work in our bodies.

Vitamin D has come a long way in a short time. When I was a medical student in the 1970s, all that was known about this nutrient was that it helped to absorb dietary calcium. It was necessary for forming bones, and lack of the vitamin gave rise to the bone diseases of rickets in children and osteomalacia in adults. Both conditions cause bones to hurt, bend and break.

We now know that every cell in our bodies contains receptors for vitamin D and that vitamin D modifies the activity of about 10,000 genes, or about one third of the human genome. Vitamin D, it seems, does an enormous amount of work in our bodies.

Once it was thought that vitamin C helped prevent everything from the common cold to cancer. That notion was largely eminence-based: The eminent Linus Pauling, winner of two Nobel prizes (chemistry in 1954, for discovering the molecular structure of vitamin C and a peace prize in 1962) widely promoted this idea.

Today, good evidence supports the idea that vitamin D not only boosts the immune system -- helping to prevent colds and flu -- but also helps regulate blood pressure and blood sugar, protect from many of the most common forms of cancer, and even possibly to help fight depression. And it still helps to make bones and muscles stronger, probably accounting for its proven role in helping prevent falls in the elderly, an often devastating and sometimes deadly problem. Indeed, a recent study showed that lower vitamin D levels are associated with higher death rates in the elderly.

Many surveys have documented the high prevalence of vitamin D deficiency in people who live in more northern locations and in people with darker skin. Indeed, pale skin allows the body to make more vitamin D when exposed to sunlight, the reason why vitamin D is sometimes called the sunshine vitamin. Our skin makes vitamin D when it's exposed to ultraviolet light from the sun.

Unfortunately, north of Atlanta, the ultraviolet light is filtered out by the atmosphere during the winter, and, as a result, vitamin D levels tend to drop as one heads north. The deficiency increases in people with dark skin, which protects from the sun's harmful effects such as wrinkles and skin cancer, but at the same time reduces our skin's production of vitamin D.

Few foods naturally contain vitamin D, although it's added to some foods including milk and some brands of orange juice. Other sources include small fish eaten whole, such as anchovies and sardines, and cod liver oil.

I'm a major advocate for vitamin D supplements. While moderate sun exposure certainly can and does boost vitamin D levels, it does so at the cost of aging the skin, which means not only wrinkles but also the possibility of skin cancer. So while moderation in all things may be a reasonable policy with regard to sun exposure, it's easier and safer, especially at northern latitudes, to take a vitamin D supplement. It is inexpensive and an excellent investment in your health.

How much is enough? This should be determined in consultation with your doctor and based upon your body's actual vitamin D level, which can be measured by a simple blood test. Because vitamin D is fat soluble, it builds up in our body's fat stores, and one can overdose on it. But doses as high as 10,000 units daily have been shown to be safe, and typical recommended doses range from roughly 1,000 to 4,000 units daily. So overdose is unlikely.

For pennies per day, this substance can help reduce falls and fractures in the elderly, prevent colds and flu, help control blood pressure and glucose levels (diabetes), and may help prevent some of the most common forms of cancer such as lung, breast, colon and prostate. African Americans suffer higher rates of such illnesses as high blood pressure, cancer and diabetes - all conditions associated with vitamin D deficiency.

As vitamin D can help reduce the incidence and severity of many conditions and disease, it could therefore help control health care costs - a major national concern. With all of its potential benefits, vitamin D is certainly worth a closer look.

For more information, read the American Public Health Association's policy statement on vitamin D at www.apha.org.

David C. Dodson, M.D., a primary care physician with the Marino Center for Integrative Health in Wellesley, Mass., is chairman of the Committee on Men's Health and a member of the Committee on Nutrition and Physical Activity of the Massachusetts Medical Society. Readers should use their personal judgment when seeking medical care and should consult with their personal physician for treatment. Physician Focus is a public service of the Massachusetts Medical Society. You are welcome to e-mail comments to PhysicianFocus@mms.org.

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